Gum, Sugar f and an Acid, ly means of S^ilphuric Acid, (ic. 123 



pTecipitate. This mucilaginous matter diflfers from that which 

 is found in the caterpillar, inasmuch as it does not dry bo ra- 

 pidly, and is resoftened by water. 



If a greater quantity of sulphuric acid is made to act a longer 

 time on the silk, different results from those which I have men- 

 tioned are obtained. 



Five grammes (77'2 gr.) of white silk cloth torn into small pieces 

 were triturated in a glass mortar, by adding succesively sidphuric 

 acid until the whole was reduced to a homogeneous mucilag** ; 

 there was a production of heat, but no sulphurous acid was dis- 

 engaged. Twenty-four hours afterwards the mixture was treated 

 with water, which produced an entire solution without precipitat- 

 ing the least particle of carbon : all that was separated was a 

 yellow flocculent matter,vvhich when dried weighed 0"I5gramme. 

 The acid liquor was saturated with carbonate of lime, and part nf 

 it reduced by evaporation, in order to favour the precipitation of 

 the sulphate of lime which it retained. The process was finished 

 by evaporating it to perfect dryness. There remained 4'2 grammes 

 of a residuum reddish and transparent resembling isinglass. 

 This residuum dissolved in a small quantity of water did not con- 

 geal by cooling. With potash it did not disengage ammonia. 

 Instilled it yielded carbonate of ammonia, and left after its inci- 

 neration sulphate of lime. The infusion of nut-galls and the 

 sub-acetate of lead precipitated it abundantly from its solution, 

 but it was only slightly precipitated by the acetate of lead. 



When therefore sulphuric acid falls upon a vestmeut of silk, 

 or linen, or of cotton, it does not burn them, as it is said; but it 

 perforates the n, and the portion affected is converted into gum- 

 my matter soluble in water. 



AcLlon of Sulphuric Acid upon Gum and Sugar. 



Gum arabic pulverized has been treated with concentrated sul- 

 phuric acid in quantity sufficient to dissolve it ; l)ut, far from pro- 

 ducing carbon, as Fourcroy pretends, the mixture was scarcely 

 coloured. At the end, however, of twenty-four hours it had con- 

 tracted a brownish colour : diluted with water, it did not preci- 

 pitate the least particle of carbon. The liquor saturated with 

 chalk produced a gum, which had exactly the same properties as 

 that which we formed by the action of sulphuric acid upon wood. 

 Exposed to the fire it burned, exhaling an odour of sulphurous 

 acid. The acetate of lead did not trouble its solution, but the 

 sub-acetate of lead produced a very abundant white coagulum. 



Cane-.sugar acted a little differently with sulphuric acid : it 

 was coloured almost immediately, and became of a blackish ma- 

 roon, which deepened in course of time ; but it did not form sul- 

 phurous acid, and tlic whole matter was entirety dissolved in 



water 



